Patent literature 1: JP 2004-251891 A (corresponding to US 2004/0195097 A1)
Patent literature 1 describes a gas concentration detection apparatus that detects AC impedance of a gas concentration sensor based on a variation in applied voltage and a variation in element current. The gas concentration detection apparatus includes an applied voltage control circuit applying a voltage to the gas concentration sensor and a current detection resistor detecting an element current.
The inventors of the present application have found the following regarding a control apparatus controlling a gas concentration sensor. The gas concentration detection apparatus described in patent literature 1 detects a variation in element current by detecting a current flowing the current detection resistor. The current is detected based on a resistance value of and a voltage across the current detection resistor. A voltage across the current detection resistor depends on a voltage applied by the applied voltage control circuit. However, the applied voltage control circuit and the current detection resistor have a manufacturing error. Such a manufacturing error may possibly deteriorate detection accuracy of the AC impedance.